B8 (304SS) vs B8M (316SS) Bolts for Marine/Offshore use

[Tim6065]

I have recently had a number of ASTM A193 B8 (304SS) Stain Hardened Bolts fail in valve bonnets on an offshore facility. The bolts are only subject to ambient tempreture; could Chloride SCC be the problem or is some other type of corrosion more likely?

Would we be better off with B8M (316SS) bolts and nuts?

 

[Duwe6]

You "got it in one". Chloride SCC, due to the strain at the root of the threads.

Switch to B7 studs/bolts, with a plastic sleeve [from an insulating flange kit, or cut from tubing] and S/S washers under the 2H nuts -- no carbon steel on the S/S valve body & flanges.